They were lower in the past. You are interpreting a dip in the "noise" level as a correlation with pot legalization. There hasn't been enough time or enough data to demonstrate such a correlation.
It sound more like you are just part of the "Yay Pot!" Cheerleading squad.
Really? Please share with us the details of the analysis of statistical (non)significance.
... Or were you just blowing smoke? (No pun intended.)
They were lower in the past.
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NHTSA contradicts you =>
Roadway deaths fall nearly 25 percent in a decade, fatality rates at a historic low
Dec 19, 2014
WASHINGTON The U.S. Department of Transportation's National Highway Traffic Safety Administration (NHTSA) today released the 2013 Fatality Analysis Reporting System (FARS) data that shows a 3.1 percent decrease from the previous year and a nearly 25 percent decline in overall highway deaths since 2004. In 2013, 32,719 people died in traffic crashes. The estimated number of people injured in crashes also declined by 2.1 percent.
http://www.nhtsa.gov/About+NHTSA/Press+Releases/2014/traffic-deaths-decline-in-2013